The invention relates to expanded carrier capacity in a mobile communications system.
Mobile communications systems, such as cellular or personal communications services (PCS) systems, are made up of a plurality of cells. Each cell provides a radio communications center in which a mobile unit establishes a call with another mobile unit or a wireline unit connected to a public switched telephone network (PSTN). Each cell includes a radio base station, with each base station connected to a mobile switching center that controls processing of calls between or among mobile units or mobile units and PSTN units.
From the original advanced mobile phone system (AMPS) standard, additional wireless protocols have been developed and implemented. One such protocol is the time-division multiple access (TDMA) protocol, originally implemented as the IS-54 standard (EIA/TIA/IS-54) and later followed by the TIA/EIA-136 protocol from the Telecommunications Industry Association (TIA). With TIA/EIA-136 TDMA, each channel carries a frame that is divided into six time slots to support up to three mobile units per channel. If half-rate voice coders are used, then each channel may be time shared among up to six mobile units. Other TDMA-based systems include Global System for Mobile (GSM) communications systems, which use a TDMA frame divided into eight time slots (or burst periods).
Traditional speech-oriented wireless systems, such as the TIA/EIA-136 and GSM TDMA systems, utilize circuit-switched connection paths in which a line is occupied for the duration of the connection between a mobile unit and the mobile switching center. Such a connection is optimum for communications that are relatively continuous, such as speech. However, data networks such as local area networks (LANs), wide area networks (WANs), and the Internet use packet-switched connections, in which communication between nodes on a communications link is by data packets. Each node occupies the communications link only for as long as the node needs to send or receive data packets. With the rapid increase in the number of cellular subscribers in conjunction with the rising popularity of communications over data networks, a packet-switched wireless data connection that provides access to the data networks, electronic mail, files in databases, and other types of data has become increasingly desirable.
Several packet-based wireless connection protocols have been proposed to provide more efficient connections between a mobile unit and a data network. One such protocol is the General Packet Radio Service (GPRS) protocol, which complements existing GSM systems. Another technology that builds upon GPRS that has been proposed is the Enhanced GPRS (EGPRS) technology, which offers higher data rates and complements GSM and TIA/EIA-136 TDMA systems.
Because of frequency spectrum limitations, the number of carriers that may be allocated for such packet-based data services in a mobile communications system may be limited. The limited number of carriers may pose a problem in regions having relatively high bursty traffic. A high bursty traffic environment is one in which a relatively high number of call setups and terminations occur during a given time period. This may occur in areas having relatively large amounts of business activity (such as in a metropolitan area) in which many users may be accessing packet-based services with their mobile telephones or other mobile units. High bursty traffic regions are contrasted with normal or low bursty traffic regions, in which relatively low numbers of call setups and terminations occur. An example of such a region is a suburban area, in which fewer calls tend to be made and in which users tend to stay connected for longer periods of time (such as to browse the Internet).
In a high bursty traffic area, the number of control bursts on each carrier may have to be increased compared to the case for normal or low bursty traffic regions to handle the increased volume of control signaling due to call setups and terminations. However, if the number of carriers used for packet-based services are limited, allocating a large number of control bursts to each carrier may reduce the amount of traffic signaling that can be carried by the carrier. This may reduce the bandwidth that is available to users for communicating packet-based traffic, which may result in slower response times.
The limited spectrum allocated for packet-based services also limits the capacity available to users. During peak usage periods, users may experience problems in gaining access to packet-based services in a given cell or cell sector.
Thus, a need exists for increasing the capacity for carrying control and traffic signaling over a packet-based wireless network.
In general, according to one embodiment, a method of communicating in a mobile communications system having a plurality of cell segments includes providing a first carrier and at least one other carrier in a first cell segment. A plurality of time slots are defined, and at least one of the time slots is allocated during which control signaling is communicated over the first carrier and the at least one other carrier.
In general, according to another embodiment, a method of providing expanded capacity in a first cell segment of a mobile communications system includes providing a first carrier for carrying control signaling in the first cell segment, the control signaling including control signaling for performing cell segment selection. A second carrier is provided for carrying signaling, the signaling not including control signaling for performing cell segment selection.
Some embodiments of the invention may have one or more of the following advantages. In regions in which extra capacity is needed in cell segments, additional carriers may be added to the cell segments within that region, which may be a region having high bursty traffic conditions or a region in which a hierarchical cell structure is desired. Increased capacity allows greater accessibility to a mobile communications system and also improves services provided to users. If extra control signaling is needed, the additional capacity is able to handle such extra control signaling without taking up bandwidth for communicating traffic.
Other features and advantages will become apparent from the following description, from the drawings, and from the claims.